I'm guessing it was the late 1990's possibly very early 2000's when I read this book, I think there was three in the series. All I can really remember is that it was about a young girl who went to a kind of magic school but there it was something about different elements like a 'chaos element' and different planes were the elements were... I think there was a cat involved too... I know it's a bit vague but if this rings a bell with anyone, and sort of help would be appreciated!
Sounds a bit like So You Want To Be A Wizard series by Diane Duane, but not quite. I don't remember enough of The Doomspell Trilogy by Cliff McNish, but there are some things you mentioned in those books.
Maybe you stand the best chance with one of Diana Wynne Jones' books, but I don't know which one. I've only read a few, and there are so many. http://www.leemac.freeserve.co.uk/books.htm